Also known as Yan Cai, Yan Root, Yan Vegetables. It is a nest made by swiftlet and a variety of swiftlets of the same genus by mixing saliva and down feathers. It is shaped like a gold ingot. The outer wall of the nest is piled up by horizontal strips of dense filaments into irregular prismatic protrusions. The inner wall of the nest is woven into an irregular network of silk, but the root of the nest is solid, with small drop angles at both ends, generally 6 to 7 cm in diameter and 3 to 4 cm in depth. Mainly produced in the South my country Sea Islands and Southeast Asian countries.